The invention relates to a method of coextruding a plate-shaped product built up from a major layer consisting substantially of a polycarbonate on which a coating layer has been provided on at least one side.
The invention also relates to the products thus obtained.
It is generally known to manufacture plate-shaped products from synthetic resins, for example, polycarbonates, by means of extrusion. For certain applications there exists a need for plate-shaped products having a matt surface. Polycarbonate itself has a shiny surface after extrusion.
In order to obtain an extruded product consisting of polycarbonate and having a matt surface, various possibilities are to be considered in principle. By incorporating certain additives, the gloss of the polycarbonate may be reduced. For example, it is known that the gloss of polycarbonate can be reduced by the addition of certain types of ABS resins. Special mattifying agents for synthetic resins are also commercially available, for example, the products based on acrylate copolymers. In order to obtain a reduction of the gloss to a value of 75% (according to ISO 2813-78) 10% by weight of ABS should be added. In practice problems occur in processing a PC-ABS (90/10) mixture: the gloss depends to a considerable extent on the extrusion conditions. It has been found experimentally that a quantity of approximately 20% by weight of acrylate copolymers has to be added to polycarbonate to reach a gloss value of 75%. However, as a result of such a large quantity the mechanical properties of the extruded product deteriorate.